Arbitration circuits are used to perform bus arbitration among a plurality of requestors (or potential bus masters) connected to the bus. In particular, the requestors transmit signals requesting access to the bus, determines which of the requestors is to be granted access to the bus, and outputs a grant to the highest priority requestor (the potential bus master which the arbitration circuit has determined will be given access to the bus). Alternatively, the arbitration circuit can transmit grant information to each of the requestors indicating, for example, the order in which the requestors will gain access to the bus. Accordingly, each of the requestors may occupy the bus and transmit data.
Known bus arbitration methods include a fixed priority method where the bus requestor having the highest priority is granted the bus, a round-robin method where the each of the requestors is given access to the bus in-turn, and a multi-level method where a group of the requestors can be given priority over other groups of requestors. In other words, in some multi-level arbitration methods, a first group can have higher priority than a second group of requestors such that if any of the requestors in the first group requests access to the bus at the same time as one of the requestors in the second group, the requestor in the first group will be given access to the bus over the requestor in the second group. It is also known to combine some of the above conventional methods as discussed, for example, in U.S. Pat. No. 6,078,338 entitled Accelerated Graphics Port Programmable Memory Access Arbiter.